I was just making reservations (just got off the phone) - the cast member inquired as to whether I was buying a package. I responded that I would like the dining, but not the ticket (I already have PAP and have frequently bought
DDP at DVC). He commented that I could buy a one day ticket - that I could elect not to use. He said it would not expire, as the expiration countdown only starts with "first use" of the pass. Then, the next time I purchase another Disney ticket - such as another AP - I could apply the single-day ticket value ($74-ish) to the AP. In other words, I wouldn't have to effectively throw away the one-day ticket just because I don't have a use for it this year.
I can't verify this from practical experience, but I can pass it along for anyone who might find it useful enough to ask their cast member in reservations.